Growers spray orchards to prevent insects and diseases from decreasing the
yield and quality of fruit. To effectively control pests and maintain quality,
the recommended pesticides must be applied at the correct time in the correct
amount to the target area. Applying pesticides effectively requires properly
calibrated application equipment and a trained operator.
This chapter describes how to calibrate an orchard sprayer and how to calculate
and adjust tree row volume.
Some factors that affect spray coverage, such as wind and humidity, are beyond the grower's control. Steps can be taken to reduce these adverse effects such as spraying during calm periods of the day or spraying when humidity is above 50 percent to help reduce evaporation of spray droplets.
Other factors that affect coverage are within the grower's control. These factors include sprayer preparation and calibration.
Check the operator's manual for information about proper and safe operation. See if the sprayer is in good mechanical condition and functioning properly. Also consider ground speed, pressure, timing, nozzle selection and placement, air speed and direction, and spray volume.
Ground speeds are usually from 2 to 5 MPH, with the most common speeds between 3 to 4 MPH. Better coverage can be obtained at the lower speeds.
Pressure in the spray system also affects coverage. Manufacturers recommend a pressure range for their machines, usually from 60 to 260 pounds per square inch.
Manufacturers also provide nozzle arrangement setups. The number of nozzles may vary from 5 to 10 nozzles per side. Nozzles should be arranged on the sprayer manifold so that two-thirds to three-quarters of the sprayer output is directed to the top half of the tree and one-third to one-quarter is directed to the lower half. Proper positioning of the air guide or director will aid in the proper placement of the spray on the target.
Nozzle size, pressure, and speed all determine spray volume. First select the desired spray volume and speed, then determine nozzle size and pressure. Spray volume may vary form 15 to 400 gallons per acre. The most common range is 50 to 150 gallons per acre.
The sprayer application rate can be determined by calibrating the sprayer before any changes are made. This is sometimes known as a trial calibration. A trial calibration is performed after the sprayer has been checked to make sure it is functioning properly and that all parts are in good condition.
During the trial calibration two things are determined: the gallons per acre (GPA) output of the sprayer and the travel speed of the sprayer.
The GPA output is obtained for a two-sided sprayer by determining the unknowns in the following formula:
Speed (MPH) and gallons per minute (GPM) output can be determine by the following procedure.
GPM = (Gallons to refill * 60 seconds per minute)/ Time to travel course (in seconds).
Example:
Known:
Now the actual GPA output of the sprayer can be determined
If you are satisfied with 200 GPA output, then mix the chemicals based on this output. But if you want to apply more or fewer GPA, determine the nozzle sizes and placement required to obtain the desired sprayer output.
Some factors that affect the sprayer output are known while other factors are unknown and must be determined and set for the machine.
Known:
Unknown
GPM output for a sprayer traveling between each row and spraying from both sides is calculated with the following equation:
Example:
Known:
Now use the following procedure to select 8 nozzles that have a combined output of half the total volume required (21.6 GPM) and that can be arranged to provide the desired volume in the top half of trees for one side; then duplicate the selection and arrangement on the other side.
Most spray nozzle manufacturers publish tables showing the GPM capacity of various nozzle sizes for various pressures. Table 6.1 is part of a manufacturer's nozzle capacity table. No single nozzle size listed in the table will provide the exact output needed. (The average output per nozzle would need to be 21.6/ 8 =2.7 GPM since only 8 nozzles can be mounted on each side of the sprayer.) The D12-45 disc and core nozzle has an output of 2.69 GPM at 150 PSI, which is extremely close.
Use 2 nozzles for the lower part of the trees:
| Orifice | Core | PSI | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| No. | No. | 10 | 15 | 20 | 25 | 30 | 40 | 60 | 80 | 100 | 150 | 200 |
| D2 | 45 | - | 0.13 | 0.14 | 0.16 | 0.18 | 0.20 | 0.25 | 0.28 | 0.32 | 0.38 | 0.44 |
| D3 | 45 | - | 0.14 | 0.17 | 0.18 | 0.20 | 0.23 | 0.28 | 0.33 | 0.36 | 0.44 | 0.51 |
| D4 | 45 | 0.18 | 0.22 | 0.25 | 0.28 | 0.31 | 0.36 | 0.43 | 0.50 | 0.56 | 0.68 | 0.78 |
| D5 | 45 | 0.23 | 0.28 | 0.32 | 0.36 | 0.39 | 0.45 | 0.55 | 0.64 | 0.71 | 0.86 | 0.99 |
| D6 | 45 | 0.29 | 0.35 | 0.41 | 0.45 | 0.50 | 0.58 | 0.72 | 0.83 | 0.93 | 1.15 | 1.33 |
| D7 | 45 | 0.33 | 0.41 | 0.48 | 0.54 | 0.59 | 0.68 | 0.84 | 0.97 | 1.11 | 1.35 | 1.57 |
| D8 | 45 | 0.41 | 0.51 | 0.59 | 0.66 | 0.72 | 0.84 | 1.04 | 1.21 | 1.35 | 1.68 | 1.94 |
| D10 | 45 | 0.54 | 0.66 | 0.77 | 0.86 | 0.94 | 1.10 | 1.35 | 1.57 | 1.77 | 2.18 | 2.50 |
| D12 | 45 | 0.67 | 0.82 | 0.95 | 1.07 | 1.17 | 1.36 | 1.68 | 1.95 | 2.20 | 2.69 | 3.11 |
| D14 | 45 | 0.75 | 0.92 | 1.07 | 1.20 | 1.32 | 1.53 | 1.89 | 2.19 | 2.45 | 3.00 | 3.49 |
| D16 | 45 | 0.86 | 1.08 | 1.25 | 1.40 | 1.54 | 1.79 | 2.20 | 2.57 | 2.89 | 3.54 | 4.11 |
| D2 | 46 | - | - | - | 0.22 | 0.24 | 0.27 | 0.33 | 0.37 | 0.42 | 0.50 | 0.57 |
| D3 | 46 | - | - | 0.23 | 0.25 | 0.28 | 0.32 | 0.39 | 0.45 | 0.51 | 0.61 | 0.70 |
| D4 | 46 | 0.28 | 0.34 | 0.39 | 0.44 | 0.48 | 0.56 | 0.68 | 0.78 | 0.88 | 1.07 | 1.23 |
| D5 | 46 | 0.38 | 0.47 | 0.54 | 0.60 | 0.66 | 0.77 | 0.94 | 1.10 | 1.25 | 1.50 | 1.73 |
| D6 | 46 | 0.55 | 0.67 | 0.78 | 0.87 | 0.95 | 1.10 | 1.35 | 1.58 | 1.73 | 2.16 | 2.50 |
| D7 | 46 | - | - | 0.98 | 1.10 | 1.22 | 1.39 | 1.72 | 1.97 | 2.22 | 2.73 | 3.15 |
| D3 | 46 | - | - | - | 1.45 | 1.59 | 1.84 | 2.25 | 2.62 | 2.93 | 3.60 | 4.17 |
| D10 | 46 | - | - | - | - | 2.15 | 2.48 | 3.05 | 3.53 | 3.96 | 4.83 | 5.59 |
Tree row volume (TRV) is a method that can be used to determine the gallons of dilute (1X) spray suspension needed to wet an orchard to the drip point. Following the initial TRV calculation, the rate per 100 gallons on the pesticide label can be used to calculate the rate of a pesticide needed per acre for a particular orchard.
TRV is based on the following formula:
This formula will give the cubic feet of foliage per acre for the orchard. For example, for an orchard with trees 18 feet tall, 14 feet wide, set on 24-foot middles,
One gallon of water will cover 1,000 cubic feet of foliage. Thus for example above, the dilute TRV base is 457 gallons per acre (GPA).
There are several adjustments to the dilute base that need to be made to account for tree density and type of pesticide application. One adjustment should be made for canopy thickness. Canopy thickness has a large effect on the amount of water needed to spray the tree to drip. Well-pruned, open trees require less water volume than trees with thicker canopies. Thus the dilute base should be adjusted using the figures in Table 6.2 as a guide. If in the previous example the tree canopy was minimally pruned (0.9), you would multiply the dilute base gallonage by 0.9 (457 GPA*0.9 = 411.3 GPA) to obtain the adjusted TRV.
A second adjustment can be made based on the type of chemical application (Table 6.3). If a pesticide was being applied in the example above, the dilute gallonage would be further adjusted by multiplying by 0.7 (411 GPA ) 0.7 = 287.9 GPA). If the base gallonage in a particular orchard is less than 200 GPA, use 200 gallons to compute the pesticide application rate per acre.
Once adjustments have been made to the dilute base, the per acre rate of a
particular pesticide can be calculated. The per 100 gallons dilute rate from
the pesticide label is used to make this calculation. For the example above, if
a pesticide was recommended at 2.0 pounds per 100 gallons, the per acre rate
would be as follows:
Once the rate per acre has been determined, this amount of pesticide can be
applied in any water volume desired. Thus, in the example above, to spray 1X
(dilute), 5.76 pounds of the fungicide would be put in 288 gallons of water
which would be applied to 1 acre. To spray 4X, 5.76 pounds of fungicide would
be put in 72 gallons of water (288 dilute base/ 4 = 72) and applied to 1 acre.
If the spray tank size was 500 gallons and the application was made at 72
gallons per acre, 40 pounds of the pesticide would be put in the tank and it
would be applied to 6.94 acres. The rate per acre determined by TRV is
completely independent of the concentration used (1X, 4X, 6X, etc).
For satisfactory disease, insect, and mite control in the Southeast, 100 gallons
per acre is generally considered a minimum for delivering the pesticide.
Turner Sutton
Table 6.2. Canopy Density Adjustments 0.70 Trees extremely open, less than 15 scaffold limbs per tree or young tree, light visible through entire tree 0.75 Trees very open, 18 to 21 scaffolds per tree, light penetration throughout tree, healthy spurs within tree canopy. 0.80 Trees well pruned, adequate light in trees for healthy spurs throughout trunk and scaffold limbs, many holes in foliage where light can be seen through tree 0.85 Tree moderately well pruned, reasonable spur population within canopy, tree thin enough that light cannot be seen through bottom two-thirds of tree. 0.90 Trees pruned minimally, spurs inside canopy weak because of limited light, very few holes where light can be seen through the tree. 0.95 Little or no pruning, spurs dead or very weak in canopy, very little light through canopy 1.00 Trees unpruned, extremely thick, no light visible anywhere through tree canopy, trees more than 20 feet high. Table 6.3. TRV Adjustments for Pesticide Type.
Type of Spray Application Percent TRV Dilute pesticide coverage 70 Promailin, Pro-Vide (as fine mist) 40 to 50 Thinners for spur Red Delicious 100 Thinners for other varieties 70 to 90 Vegetative growth inhibitor application 100 Preharvest ethrel and stop-drop 100 to 120 Calculating the Per Acre Application Rate